optimization of injection moulding process for hdpe...
TRANSCRIPT
OPTIMIZATION OF INJECTION MOULDING PROCESS FOR HDPE
MOULDED GEAR
by
MOHD SYAHIR BIN MOHD KASSIM
A Thesis Submitted in Partial Fulfilment of the
Requirement for the Degree of
Master of Science
JULY 2015
ii
ACKNOWLEDGEMENT
Alhamdulillah, through His Blessing and Dignity of Allah s.w.t. allowed me
complete this thesis. I express my sincere gratitude to my supervisor, Assoc. Prof
Dr. Shahrul B. Kamaruddin, for their endless guidance, support and encouragement
towards completion of this research. Without his guidance and motivation, I could
not have finished this dissertation.
The assistance from my colleagues; Nik Mizamzul Bt Mehat and Amirul
Aliff Bin Jamaluddin is valuable for their help on perfecting my experiment plan and
solving many related problems. Also special appreciation to all staff in Mechanical
Engineering Department, USM for their help and support at work especially Mr.
Syawal Faizal for his machine and mould setup.
I express my heartfelt gratitude to my beloved family mainly my father Mohd
Kassim Shaik Mohd who give me moral support and inspiration. Finally, I would
like to express my appreciation to Ministry of Higher Education, Mybrain15, for
funding my tuition fees as well as USM research grant that providing me allowances
during my study.
Mohd Syahir Bin Mohd Kassim
JULY 2015
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TABLE OF CONTENTS
Contents
ACKNOWLEDGEMENT ........................................................................................... ii
TABLE OF CONTENTS ............................................................................................ iii
LIST OF TABLES ...................................................................................................... vi
LIST OF FIGURES .................................................................................................. viii
LIST OF ABBREVIATIONS ...................................................................................... x
ABSTRAK ................................................................................................................. xii
ABSTRACT .............................................................................................................. xiv
CHAPTER 1 ................................................................................................................ 1
1.0 Overview ........................................................................................................... 1
1.1 Research Background........................................................................................ 1
1.2 Plastic Recycling ............................................................................................... 2
1.3 Injection Moulding ............................................................................................ 4
1.4 Problem Statement ............................................................................................ 4
1.5 Research Objectives .......................................................................................... 5
1.6 Research Scope ................................................................................................. 6
1.7 Thesis Outline ................................................................................................... 7
CHAPTER 2 ................................................................................................................ 8
2.0 Overview ........................................................................................................... 8
2.1 Plastic Overview ............................................................................................... 8
2.2 Plastics Recycling ........................................................................................... 10
2.3 Limitations of Recycled Plastic ...................................................................... 13
2.4 Plastic Gear ..................................................................................................... 14
2.5 Plastic Gear Manufacture ................................................................................ 16
2.5.1 Injection Moulding Process ..................................................................... 17
2.5.2 Influential Factors on Injection Moulded Quality ................................... 19
2.6 Optimization Method ...................................................................................... 24
2.6.1 Taguchi Method ....................................................................................... 25
iv
2.6.2 A Review on the Previous Works of Taguchi Method ............................ 27
2.6.3 Principal Component Analysis ................................................................ 29
2.6.4 Integration Taguchi Method with Principal Component Analysis (PCA)32
2.7 Findings from the Literature ........................................................................... 34
CHAPTER 3 .............................................................................................................. 37
3.0 Overview ......................................................................................................... 37
3.1 Materials .......................................................................................................... 37
3.2 Product Part Description ................................................................................. 38
3.3 Screening Experiment ..................................................................................... 39
3.3.1 Determining the Quality of Characteristics ............................................. 41
3.3.2 Selection of Processing Parameters ......................................................... 41
3.3.3 Selection of Orthogonal Array (OA) ....................................................... 42
3.3.4 Quality Testing ........................................................................................ 43
3.3.5 Analysis of Screening Experiment .......................................................... 46
3.4 Optimization Experiment ................................................................................ 50
3.4.1 Selection of Orthogonal Array (OA) ....................................................... 52
3.4.2 Quality Testing ........................................................................................ 54
3.4.3 Analysis of Optimization ......................................................................... 55
3.4.4 Confirmation Test .................................................................................... 62
3.5 Feasibility Experiment .................................................................................... 62
3.5.1 Quality Testing of Recycled HDPE Plastic Gear .................................... 67
3.5.2 Analysis of Quality Performance on Recycled HDPE Moulded Gear .... 68
3.6 Summary ......................................................................................................... 69
CHAPTER 4 .............................................................................................................. 70
4.0 Overview ......................................................................................................... 70
4.1 Screening Experiment ..................................................................................... 70
4.1.1 Signal to Noise Ratio ............................................................................... 72
4.1.2 Analysis Of Variance (ANOVA) ............................................................. 73
4.1.3 Result of Screening Experiment .............................................................. 81
4.2 Optimization Experiment ................................................................................ 82
4.2.1 S/N Ratio and Normalization ................................................................... 85
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4.2.2 Principal Component Analysis, PCA....................................................... 88
4.2.3 Main Effect Analysis and Optimization on MQCI .................................. 92
4.2.4 Interaction Effect Analysis ...................................................................... 95
4.2.5 ANOVA of MQCI ................................................................................... 99
4.2.6 Prediction of Optimal Process Condition .............................................. 101
4.3 Confirmation Test of Optimal Combination Result ...................................... 102
4.4 The Feasibility of Multiple Reprocessing ..................................................... 104
4.4.1 Rheological Analysis ............................................................................. 105
4.4.2 Thermal Analysis ................................................................................... 106
4.4.3 Thermal Stability Test ........................................................................... 107
4.4.4 Quality Effect of Multiple Recycle Moulded Gear Test........................ 108
4.5 Summary ....................................................................................................... 112
CHAPTER 5 ............................................................................................................ 113
5.0 Overview ....................................................................................................... 113
5.1 Conclusion .................................................................................................... 113
5.2 Recommendation for Future Works .............................................................. 116
REFERENCES ......................................................................................................... 118
APPENDIX - A ........................................................................................................ 128
APPENDIX - B ........................................................................................................ 129
APPENDIX - C ........................................................................................................ 130
vi
LIST OF TABLES
Page
Table 3.1 General Properties of High Density of Polyethylene ............................ 38
Table 3.2 Processing Parameter and Levels ......................................................... 42
Table 3.3 Taguchi's Orthogonal Array L18 ........................................................... 43
Table 3.4 Orthogonal Array of L27 with Interaction Effect ................................... 53
Table 4.1 Processing Parameter for Screening Experiment .................................. 71
Table 4.2 Screening Experiment Setup via L18 OA .............................................. 71
Table 4.3 S/N Ratios of Experiment Results ........................................................ 72
Table 4.4 ANOVA for Addendum Shrinkage ...................................................... 76
Table 4.5 ANOVA for Dedendum Shrinkage....................................................... 77
Table 4.6 ANOVA for Tooth Thickness Shrinkage ............................................. 77
Table 4.7 ANOVA for Ultimate Strength ............................................................. 78
Table 4.8 ANOVA for Modulus Young ............................................................... 79
Table 4.9 ANOVA for Elongation at Maximum Load ......................................... 80
Table 4.10 Screening Result of Significant Parameters .......................................... 82
Table 4.11 Processing Parameter for Optimization Experiment ............................ 83
Table 4.12 Optimization Experiment Setup via L27 OA ......................................... 84
Table 4.13 Responses of Optimization Experiment ............................................... 85
Table 4.14 S/N Ratios of the Optimization Experiment Results ............................ 86
Table 4.15 Normalization of Optimization Experiment Result .............................. 87
Table 4.16 Correlation Coefficient Matrix of the Multiple Quality
Characteristics ....................................................................................... 89
Table 4.17 Eigenvalues, Proportion Explained, and Cumulative Total .................. 89
Table 4.18 Eigenvectors Corresponding to the Eigenvalues .................................. 89
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Table 4.19 Principal Component Scores and Total PC Score as the
Multiple Quality Characteristics Indices (MQCI) ................................ 91
Table 4.20 Main Effect Performance on Multiple Quality Characteristic
Indices ................................................................................................... 93
Table 4.21 Interaction Effect of Melting Temperature and Mould
Temperature .......................................................................................... 97
Table 4.22 Interaction Effect of Melting Temperature and Cooling Time ............. 97
Table 4.23 Interaction Effect of Mould Temperature and Cooling Time ............... 98
Table 4.24 ANOVA for MQCI with Interaction Effect ........................................ 100
Table 4.25 Result of Confirmation Test for Multiple Quality
Characteristic ...................................................................................... 103
Table 4.26 Quality of Moulded Gear for Recycled HDPE ................................... 109
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LIST OF FIGURES
Page
Figure 3.1 Geometry and Specification of Spur Gear ............................................ 38
Figure 3.2 Flow Chart of Screening Experiment ................................................... 40
Figure 3.3 Fixture for Tensile Test ......................................................................... 46
Figure 3.4 Flow Chart of Optimization Experiment .............................................. 51
Figure 3.5 Flow Chart of Feasibility Experiment .................................................. 63
Figure 3.6 Melt Flow Index Equipment ................................................................. 65
Figure 3.7 TA-Q20 Differential Scanning Calorimeter ......................................... 66
Figure 3.8 Perkin-Elmer Pyris 1 TGA ................................................................... 67
Figure 4.1 Main Effect Plots of MQCI .................................................................. 93
Figure 4.2 Interaction Effects Plot of Melting Temperature and Mould
Temperature .......................................................................................... 97
Figure 4.3 Interaction Effects Plot of Melting Temperature and Cooling
Time ...................................................................................................... 98
Figure 4.4 Interaction Effects Plot of Mould Temperature and Cooling
Time ...................................................................................................... 99
Figure 4.5 Melt Flow Index toward 15th Recycles of HDPE .............................. 105
Figure 4.6 Graph of Melting Temperature and Percentage of Crystallinity
of HDPE .............................................................................................. 107
Figure 4.7 Graph Thermal Stability of HDPE toward Number of Recycle ......... 108
Figure 4.8 Shrinkage Rate of Moulded Gear toward Number of Recycle ........... 109
ix
Figure 4.9 Ultimate Strength of HDPE Moulded Gear toward Number of
Recycle ................................................................................................ 110
Figure 4.10 Modulus Young of HDPE Moulded Gear toward Number of
Recycle ................................................................................................ 110
Figure 4.11 Elongation at Maximum Load of HDPE moulded Gear toward
Number of Recycle ............................................................................. 111
x
LIST OF ABBREVIATIONS
AGMA American Gears Manufacturers Association
ANOVA Analysis of Variance
CAD Computer-Aided Engineering
CRS Conventional Runner Systems
DOE Design of Experiment
DOF Degree of Freedom
DSC Differential Scanning Calorimeter
EPDM Ethylene–Propylene–Diene Terpolymer
HDPE High Density Polyethylene
HRS Hot Runner System
LDPE Low Density Polyethylene
MPI Multi Performance Index
MQCI Multiple Quality Characteristics Index
MSW Municipal Solid Waste
OA Orthogonal Array
PA Polyamide
PCA Principle Component Analysis
PIW Post-Industrial Wastes
PP Polypropylene
S/N Signal-to-Noise
SAW Submerge Arc Weld
SRT Scrap Rubber Tires
Tdec Decompose Temperature
TGA Thermal Gravimetric Analysis
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Tonset Onset Temperature
WPCA Weighted Principle Component Analysis
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PENGOPTIMUMAN PROSES SUNTIKAN ACUAN TERHADAP HDPE
GEAR
ABSTRAK
Pada masa kini, penggunaan plastik seluruh dunia meningkat secara mendadak dalam
pelbagai applikasi produk. Berikutan permintaan, pengeluaran yang pantas
diperlukan untuk menampung keperluan pasaran. Oleh kerana itu, semua pengilang
plastik berusaha keras untuk mengekalkan kualiti produk dan pengilang juga
dibebani dengan masalah pengurusan sisa plastik yang berkaitan dengan perlupusan
sisa post-industri yang cekap. Pelbagai usaha telah dilakukan untuk memudahkan
kitar semula plastik ke tahap yang lebih bagus dalam menyelesaikan isu pelupusan
plastik serta peningkatan kualiti produk. Dalam kajian ini, kebolehlaksanaan proses
berkala kitar semula HDPE dikaji berdasarkan ciri-ciri kestabilan dimensi, sifat
mekanikal dan reologi bahan. Pengoptimuman proses parameter acuan suntikan
terhadap gear HDPE telah dilaksanakan melalui kaedah integrasi Taguchi dan
prinsipal komponen analisis (PCA). Penilaian prestasi mengambil kira fungsi pada
gear plastik, kadar pengecutan dan sifat pemanjangan bahan. Eksperimen saringan
telah dilakukan dengan susunan ortogon L18 untuk proses penyaringan parameter
beerti yang terlibat. Kemudian, parameter yang optimal dan kesan interaksi
parameter telah dikenal pasti melalui pengoptimuman eksperimen dengan
menggunakan L27 OA, PCA, analisis kesan utama dan analisis varians (ANOVA).
Keputusan mendapati, kadar pengecutan dan sifat tegangan pada gear HDPE dapat
dioptimumkan secara serentak. Akhir sekali, parameter optimum yang diperolehi
telah digunakan dalam eksperimen kebolehlaksaan untuk penilaian prestasi kitar
semula berkala untuk HDPE. Keputusan mendapati bahawa pemprosesan kitar
semula berkala pada peringkat ke-3 hingga ke-7 mempunyai prestasi yang optimum
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di mana prestasi ia hampir sama dengan prestasi HDPE yang asal. Hasil daripada
penyelidikan ini menunjukan bahawa keberkesanan integrasi kaedah Taguchi dengan
PCA telah terbukti dalam pengoptimumam proses parameter dan pelbagai kualiti
dalam HDPE gear telah dapat ditingkatkan secara serentak dengan bilangan nombor
eksperimen yang rendah.
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OPTIMIZATION OF INJECTION MOULDING PROCESS FOR HDPE
MOULDED GEAR
ABSTRACT
Nowadays, the world's plastic usage has drastically increased in various applications
of product. As demand, a high speed production is requires to sustain the market
needs. Consequently, all plastic manufacturers are struggling to maintain the quality
of moulded product and they are also burdened with plastic waste management
issues related to the efficient disposal of the post-industrial waste. Numerous efforts
have been done to facilitate the plastic recycling to a greater extent in solving the
plastic disposal issues as well as quality improvement of moulded product. In this
research, the feasibility of multiple recycle HDPE is investigated based on their
dimensional stability, mechanical and rheological properties. The optimization of the
injection moulding processing parameters for HDPE gear is presented via integration
of Taguchi method with principal component analysis (PCA). Considering the
functionality of the plastic gear, the shrinkage rate (tooth thickness, addendum and
dedendum circle) and tensile properties (ultimate strength, Modulus Young, and
elongation at maximum load) are selected as the performance response. A screening
experiment was conducted with an L18 orthogonal array (OA) to screen out the
significant parameters involved. Later, the optimal parameters and interaction effect
is identified via optimization experiment with the used of L27 OA, PCA, main effect
analysis and analysis of variances (ANOVA). As a result, the shrinkage
characteristics and tensile properties of moulded gear are optimized simultaneously.
Finally, the obtained optimal parameter settings were used in feasibility experiment
in order to evaluate the performance of multiple recycle HDPE. The results depict
xv
that reprocess cycle at 3rd to 7th have the optimal condition which closes to virgin
HDPE performance. The experimental findings show the effectiveness of the
integration Taguchi method with PCA in optimizing parameter settings has proved
and also improve the multiple quality characteristics of HDPE moulded gear
simultaneously with minimum number of experiment.
1
CHAPTER 1
INTRODUCTION
1.0 Overview
This chapter describes the research background including the plastic
recycling injection moulding and the problem statement. Subsequently, the research
objectives and scope has been explained. Finally, the thesis outline has been
discussed in this chapter.
1.1 Research Background
The revolution of the industrial plastic is believed to have started around
1800s and it has attracted more attention of researchers in plastic development since
it was introduced. In 1856, the first plastic was patented as 'Parkesine' by Alexander
Parkes, a British metallurgist who introduced an organic material cellulose treated
with solvent of nitric acid to create plastic (Fenichell, 1996). Later, an American
researcher, John Wesley Hyatt has successfully created plastic in year 1869 with
celluloid, where it has derived from cellulose and alcoholized camphor (McCord,
1964). Over a few decades, plastic material has been modified chemically for
improvement and finally it was derived into synthetic material or known as modern
plastic.
The development of plastic offers more benefits to human life in various
applications of product because of their natural properties such as lightweight,
durability and versatility. Due to these characteristics, plastic demand has increased
drastically around the world to replace other materials to fulfil market needs from
2
simple product such as storage container, to sophisticated product such as heart
replacement valve. In fact, with a wide range of properties with low cost of raw
material, the global plastic production is significantly increased over 260 million tons
by today. The quantities of plastics have been estimated will be reach at least 19
billion tons annually by 2025 (Yoshizawa et al., 2004). However, the excessive
plastic product usage has directly increased the plastic waste. Additionally,
inefficient plastic waste management has contributed to environmental issues in our
life. Various approaches have been applied in plastic waste management such as
recycling, landfill and incineration to overcome the plastic waste issue (Lazarevic et
al., 2010). Due to limited space of landfill and non biodegradable plastic waste,
landfill method is not really efficient to solve the problem of plastic waste, which
takes a long period to decompose. Besides, incineration of plastic waste will release
hazardous gasses that will affect the environmental and also human health. Realizing
of these limitations of landfill and incineration method, recycling approach is
considered to be used to solve plastic waste issues.
1.2 Plastic Recycling
Currently, the plastic waste management has been considered as a vital issue
for Malaysian government due to the increasing population and the Malaysian
lifestyle that contributes to environmental issues. Various efforts have been done to
give awareness of the public about plastic recycling. Plastic recycling is the most
effective method to manage plastic waste compared to the landfill and incineration
waste disposal methods. Many studies have proven that plastic recycle products
highly beneficial to the society, economic and environment as well (Ahmad &
Mayamin, 2012).
3
The application of recycled plastic significantly can reduce the consumption
of petroleum and preserve the limited resources. In fact, most of plastics are
produced from fossil fuel or natural gas. The production of plastics needs 8% of the
world's annual oil production as a feedstock, where 4% from that amount is used in
energy consumption of plastic process (Plastic Ocean, 2010). Besides, the recycled
plastic material can saved up to 70% of energy consumed in the process plant in
terms of electricity or fuel compared to virgin resins production (Santos & Prezzin,
2003). If all these factors are considered, the recycling of plastic waste would be
efficient.
To date, the government authority has restricted the environment regulations
to all plastic manufacturers in order to comply the ISO14001 in preventing pollution.
Manufacturers need to considering the green productions in order to facilitate the
plastic recycle process to a greater extent. Nevertheless, a large scale of recycled
plastic has been doubted to be good replacement of virgin plastics. The changes of
material properties in plastic recycling such as mechanical and rheological properties
have created a bad perception that plastic recycling has produced low quality
products. Therefore, most of manufacturers prefer a virgin resin plastic in their
production rather than recycled resin plastic. Indeed, the properties of recycled
plastic tend to decrease after several reprocessing cycles (Balart et al., 2005).
However, the improvement quality of recycled plastic product could be made via
optimization processing parameters in order to find optimal performance with
satisfactory quality.
4
1.3 Injection Moulding
Injection moulding is one of the common methods used in plastic
manufacturing process for fabrication of plastic part with a great dimensional
tolerance; vary size product and complexity. Growing demands on plastic product
requires high speed production line to sustain market needs. The quality product will
be the first priority in manufacturing process to avoid rejected part and loss of profit.
To achieve a good quality product, several factors needs to be considered in term of
materials, injection machine, mould design and process parameter setting.
In view of process control, processing parameters of injection moulding can
be classified into four groups; temperature, time, pressure and distance. The quality
of moulded part fluctuates within a particular range due to incompatible input
parameters setting (Alireza & Mohammad, 2011). Moreover, the interaction effect
analysis of particular parameters is required in determining the relationship between
the parameters. Therefore, finding the optimized parameters is most desirable in
injection moulding process in order to achieve a good quality performance of
moulded parts.
1.4 Problem Statement
In the injection moulding industry, the processing parameter setting
significantly influences the quality of moulded product. Previously, trial and error
method is used in determining the optimal parameters settings. However, this
method is not systematic and it involves high cost of operation. The optimization
process parameter requires multidisciplinary knowledge and more systematic method
to replace the trial and error method which causes consuming time, high cost and
needs extra works. This issue has been raised among plastic manufacturers to find
5
out an efficient optimization approach which has the ability to optimize multiple
quality characteristics of moulded parts. Therefore, this study proposes an efficient
optimization method of injection moulding process parameter.
Regarding the plastic recycle issues, many plastic manufacturers have
interest to utilize plastic recycle material into their plastic fabrication in order to
reduce production cost. Usually the plastic recycle properties have improved via
blending method, either blending with virgin material or other different materials.
However, is it possible for multiple recycles of polymer to be able to provide a good
quality of moulded part? Hence, an alternative effort has been done in this study to
investigate the feasibility and quality finished product of multiple reprocessing of
HDPE plastic material toward optimize processing parameter.
1.5 Research Objectives
The objectives of this research can be describes as;
1. To optimize the processing parameters of injection moulding in order to
achieve the optimal quality performance of moulded gear.
2. To study the effectiveness of integrated Taguchi method with Principal
Component Analysis in optimizing multiple quality characteristics of
moulded part.
3. To investigate the feasibility and quality finished product of multiple recycle
plastic towards optimized processing parameter.
6
1.6 Research Scope
In view of plastic waste management, there are two types of plastic waste that
can be classified; post-consumer waste and post-industrial waste. In this study, the
post-industrial waste is preferred due to its purity of material and the possibility of
contamination material is less. Additionally, plastic type is restricted to
thermoplastic because of their recyclable properties, which has the ability to undergo
the reheating process. Considering the common thermoplastic material, High
Density Polyethylene (HDPE) is selected as the main material for fabricating
moulded gear. To limit scope of study, the recycle material is prepared from virgin
material scraps and it is used repeatable for 15 reprocessing cycles.
Considering the application of plastic gear, the dimensional stability and
mechanical properties of gear have been selected to be analyzed for quality
improvement. Due to the complexity of geometry, the injection moulding process is
used to produce the moulded gear via numerous parameters settings. The significant
processing parameter of injection moulding is analyzed in order to obtain the optimal
performance of quality characteristic moulded gear. The integrated of Taguchi
method and principal component analysis (PCA) were utilized in the optimization
process of multiple quality characteristics performance.
7
1.7 Thesis Outline
This thesis covers five chapters which include introduction, literature review,
methodology, result and discussion, and conclusion. Chapter 1 in briefly discusses
the research background which is related to plastic development, the issue of plastic
waste management, injection moulding, plastic product quality and processing
parameter. Moreover, the problem statement and objectives of this research are also
mentioned in this chapter. Chapter 2 discussed the current knowledge and studies
from other researchers that are related to fundamental of plastic, plastic recycling,
injection moulding process, improvement quality of moulded plastic and
optimization of process parameter. Chapter 3 describes the methodology used in this
research where the procedure is explained in detail including the screening,
optimization and feasibility of experiment. Chapter 4 analyses and discusses the
result obtained from experiments based on optimization of processing parameters
toward quality moulded gear. The feasibility experiment analyzes the effect of
recycles material toward the quality of moulded gear. Finally, chapter 5 highlights
the conclusion of research work in this chapter and ends with recommendations for
future work.
8
CHAPTER 2
LITERITURE REVIEW
2.0 Overview
This chapter begins with a brief discussion about plastic material, their
consumption and their impact on environmental issues. Later, the following sub-
section described the matters on plastic recycling including the limitation on the uses
of recycled plastic. Considering the gear as a main subject to be pertinent with plastic
applications, the details on plastic gear will be review thoroughly on subsequent sub-
section. An introduction to numerous of plastic gear’s processing method is
presented and the injection moulding process is highlighted as a main focus to be
discussed in this study. Subsequently, the influences of material selection, mould
and product shapes design as well as processing parameters in affecting the quality of
produced parts has been reviewed. Previous work relating with standalone Taguchi
method and integration of Taguchi method with principle component analysis (PCA)
will be reviewed thoroughly. Finally, the findings from the literature review will be
concluded at the end of this chapter.
2.1 Plastic Overview
“Plastic” was defined as a type of high molecular mass synthetic polymers
(American Chemistry Council, 2012). Generally, plastics are formed from the
organic natural resources originated from the synthesis of plants or petrochemicals
substances and it can be classified into two types: thermosetting and thermoplastic.
Thermosets is a synthetic polymer that cannot be reprocessed once it was used during
9
manufacturing process. However, thermoplastic has a contra characteristic with
thermoset material. Thermoplastic is a synthetic polymers that can be recurrently
reheated over and over against without undergoes any substantial chemical change.
The variability and versatility of plastic materials have allowed themselves to meet
specific technical requirements for particular applications.
Plastic’s product manufacturing is one of the most growth industries in the
world. The unique characteristics of plastics, such as durable, lightweight and
inexpensive are very attractive to be used as a daily consumer’s product. Plastics
application has highly penetrated into multi-purpose application such as in producing
the electric and electronic parts, household, packaging material, automotive part,
construction material, medical tool and many more. According to Jose (2012),
Global Industry Analysts Incorporation has reported that the global plastic
consumption will reach approximately 297.5 million tons by 2015. Moreover, it was
expected that the global plastics consumption will grow for 4% per year from 2010
to 2016. Obviously, the aforementioned statistic has figured out that plastics have
become an important material in our daily life application.
Unfortunately, the huge amount of plastics consumption has raised a critical
issues related to the environmental conservation problems. The non-biodegradability
properties of plastic materials lead to the increasing amount of plastic wastes and
become a major threat particularly on land pollution problems since it probably takes
a decade to completely decompose. According to U.S. Environmental Protection
Agency (2014), there are 32 million tons of plastic waste were generated in 2012,
which accounts for 12.7% of total municipal solid waste (MSW) where 14 million
tons of plastics are packaging and containers, 11 million tons are durable goods and 7
10
million tons are nondurable goods. It is very difficult and costly to manage such a
huge amount of plastic wastes.
Hence, there is necessary to find the best solution for a sustainable plastic
waste management strategy to properly manage the huge amount of plastic materials
that piled in the waste stream. At present, the landfill disposal method and
incineration method is not more relevant due to the limitation of land filling space
availability and an emission of dangerous gaseous that can harm human health.
Therefore recycling is identified as the best solution for plastic wastes management
with the advantage in pollution reduction as well as effective reduction of fossil
energy consumption.
2.2 Plastics Recycling
Since plastic was introduced in 1940s, the plastic’s production and
consumption was increase drastically due to high demands all around the world for
various applications in order to fulfil the current needs. Consequently, plastic solid
wastes disposal has increased instantly. Thus, the plastic recycling approach has
promise a best solution in reducing the rate of plastic wastes disposal, reduces the
issues on the landfill’s space problem as well as reduction in the emission of harmful
gaseous through incineration process. According to Fei (2013), plastic wastes can be
divided into two categories consist of post-consumer wastes and post-industrial
wastes. Post-consumer waste can be referred as the wastes that generated by
surrounding consumers especially by the peoples in residential area. Generally, post-
consumer plastic wastes are contaminated with other foreign materials and need to be
segregated before the recycling process can be performed (Takoungsakdakun &
Pongstabodee, 2007). On the other hand, post-industrial wastes are referred as the
11
process scrap parts such as sprues, runners and defect parts that are not contributing
into production. In contrary to post-consumer plastic wastes, the post-industrial
plastic wastes are relatively clean since it consists of homogenous materials type.
Therefore, the compatibility problem should not be an issue in this post-industrial
plastic wastes recycling process.
Generally, plastic recycling process can be divided into four major categories;
primary, secondary, tertiary and quaternary. Each category provides a particular
benefit and advantage for specific requirement.
i. Primary recycling
Primary recycling is known as a closed loop recycling method. The disposed
polymers such as drinking bottle and oil container is collected and reprocessed to
their original use with similar properties (Al-Salem 2009). However, the plastic
wastes should be properly segregated since this primary recycling only compromise
for clean and homogenous plastics type.
ii. Secondary recycling
Secondary recycling process is referred to an open loop recycling process that
involved the altering of mechanical or physical properties of new produced products
(Mastellone, 1999). In fact, the wastes used in this secondary process consist of
heterogeneous plastics type that commonly contaminated with other post-consumers
materials. Therefore, the recycled product’s performance is downgraded due to the
existences of impurities and incompatibility issues.
12
iii. Tertiary recycling
Tertiary recycling process is knows as feedstock or commonly known as
chemical recycling. This type of recycling process involve an advance processing
approach by converting polymer wastes into low molecular weight, monomers or
valuable chemical for petrochemical stock (Cardona & Corma, 2000). Common
process involved for tertiary recycling process is chemical depolymerisation and
thermal decomposition reaction. However, it is very costly and limited to be applied
for commercial purpose due to economical consideration.
iv. Quaternary recycling
Quaternary recycling or energetic recycling is a process that involved the
energy recovery by plastic wastes combustion as a source to generate electricity (Ha
& Kyung, 2012). However, the plastic that is derived from crude oil may contain a
very high calorific composition and it will release several of harmful gaseous such as
dibenzofurans which irritated to human and environment health. Although it offers
several advantages for energy recovery purpose, this quaternary recycling process is
considered as the last method option for plastic wastes annihilation due to health and
safety issues.
The classification of recycling process is clearly discussed in this section and
it is very useful to recognize the type of recycling process that is involved in this
study. Besides, the recycling material has several limitation in order to maintain the
performance of quality material same as virgin material. This issue will discuss in
the next section.
13
2.3 Limitations of Recycled Plastic
The biggest challenge of recycling process is to maintain the polymer
performance within levels, which allow the material reuse in the same or other
particular purpose. Almost all established plastic industry are preferred the virgin
plastic resin to ensure and secure the properties of the material meet their product
requirement especially in food packaging sector, medical tool and for baby product
(Eureka Recycling, 2009). Although plastic waste undergoes several recycle process
and a comprehensive treatments is needed to ensure it as pure as possible.
Basically the properties of recycled plastic have changes after recycling
process particularly on physical properties such as material purity, thermal and
mechanical properties. This phenomenon occur during reprocessing operation that is
caused degradation effect and directly change the molecular structure where it gives
side effect on the mechanical performance and on the rheological characteristics
(Scaffaro, 2012).
Contamination with impurities material often appears on recycling plastic
because uncontrolled waste material during segregation process. The contamination
recycled plastic are referred in various form such as dirt, partially oxidized polymers,
printing inks, paper, pesticides, metals, additives and so on (Scheirs 1996). Normally
it happens to post-consumer waste because they are not classified the plastic waste
properly follow their type and mixed with other element. Ruifeng and Rakesh
(2001) were claimed in their study that 1% impurity of polymeric have enough to
decrease certain mechanical properties. It means more than 99% purity of polymer is
needed to sustain their originality of material properties. In addition, the blending of
difference types of polymer could be treated as impurity because the microstructure
14
it formed, incompatible each other and contribute the fraction in microstructure.
Mathew and Thomas (2003) has proved in their study that incompatible blending
polymer can induces the poor adhesion of microstructure and the polymeric fraction
which influences the performance of material properties.
Thermal degradation is also one of the effects in polymer recycling process.
Generally, thermal degradation occurred when the polymer is overheated exceeding
the service temperature until the primary chemical bonding are separated or known
as molecular scission (Van & Klass, 2009). Once the microstructure of the polymer
is changes due to thermal degradation, there has some effect are induced on their
important mechanical properties such as stiffness, tensile strength and impact
resistance (Moeller, 2008). Vilapna et al. (2006) discovered in their study that multi
recycle polymer will alter the oxidative stability in polymer, hence it significantly
influence the elongation properties of material. Besides, Karahaloiu and Tarantili
(2009) also agreed that thermal degradation occur during reprocessing polymer will
induced the microstructure chain scission and influences the mechanical and
rheological performance of material.
2.4 Plastic Gear
The term 'gear' can be considered as a basic component of machine in
human's life application. The revolution of gears application is begins since the
invention of rotating machinery that used in generating power and motion transfer
(Drago, 1998). The gear applications have received a special attention around the
world due to their unique features in term of technical operation. At the beginning of
creation, the gears have been made from wood. In eighteenth century, during the
British industrial revolution, the metal gear design and manufacturing is rapidly
15
developed. Indeed, the development of gear technology is keep expanding till today
especially in materials and design improvement. Modern metallurgy is significantly
contributed to the variety of gear application; i.e. in the automotive industry as well
as electric and electronic devices (Mallesh et al., 2009).
Currently, the performance of plastic gear have achieved a new level in
developing process to replace the metal gears in various application from large
component to micro and nano-scales of electronic devices (Hakimian & Sulong,
2012). Most of technical community are prefer the plastic gear in machine
applications due to several features, such as lubricant-free, silent operation and
lightweight properties (Lin & Kuang, 2008). The advances of materials and
moulding technology have successfully lead the better performance of plastic gear in
carrying load motion and power transmission (Kim, 2006).
According to Mendi et al. (2006), the failure mechanisms of plastic gear have
been exhibited similar to metal gear, for example an excessive wear, creep, tooth
fatigue and deformation. However, the limitations of plastic gear and metal gear are
able distinguished through their performance. In facts, the plastic gears have poor
properties in term of mechanical, thermal resistance, load-carrying capacity, service
life and modulus elasticity compared to metal gear (Senthilvelan & Gnanamoorthy,
2006). Due to these properties, the plastic gear applications are limit and unable to
sustain a high load capacity and accumulated heat.
Over a few decades, a numbers of studies have been conducted to analyse the
quality of material and failure mechanisms of plastic gear during operation. Ikegami
et al. (1986) studied the plastic gear material performance on mechanical strength of
glass and carbon roving clothes reinforcement. The finding shows the glass
16
reinforcement is significantly improved the bending strength of plastic gears.
Otherwise, Yakut et al. (2009) investigated the capabilities of plastic gear in resisting
load through a meshing method. As a result, the meshing gears of different polymer
PC/ABS can resist a high load capacity compared to homogeneous polymer PC/PC
and ABS/ABS. Moreover, the modification of plastic gear has been made to
improve the gear performance. Düzcükoğlu (2009) investigated the thermal
distribution on tooth surface of polyamide gear. The cooling holes were drilled at
different location on tooth surface for the purpose of distributing the generated heat.
The results showed, the modified design is successful to decrease the temperature of
tooth surface and wear resistance has been improved. In other works, İmrek (2009)
modified the teeth width of Nylon6 spur gear in order to investigate the gear damage.
From this study, the author found that modified Nylon 6 gears exhibited lower tooth
temperatures and decreased in wear rate.
Most of study was reported on performance of material and gear design
modification (Wright & Kukureka, 2001). However, the study about effect of
manufacturing process in gear making is rarely done. In obtaining a good quality of
plastic gear, advances knowledge of manufacturing process is required. Therefore,
this study emphasized the manufacturing process of plastic gear for better
improvement and it will further discuss in next section.
2.5 Plastic Gear Manufacture
Generally, plastic gears are able to be manufactured via two main methods;
either machining (removal process) or injection moulding (forming process). The
machining process of plastic gear is done similarly to process used in machining of
metal gears. According to Davis (2005), there are several reason to be considered
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machining process over moulding as the manufacturing process of plastic gear; the
small quantities of produced gear is required to justify the tooling cost for moulding
process, complex gear design with a high dimensional tolerance may be too difficult
for moulding, unsuitable plastic materials for moulding process.
However, the produced plastic gear of machining process invariably leave
gear teeth with different strengths, wear resistance and chemical resistance. For
these reasons, the injection moulding is more preferable method in manufacturing of
plastic gear. Besides, the material used in machining process may expose to void
especially for fibrous material such as glass or carbon fibre, when it is used as
additives in moulded gears. The additives may be removed during machining
process and the surface of material will leave openings. Comprehending to these
facts, the injection moulding method is selected process in this study for plastic gear
manufacturing process. Understanding the injection moulding process is needed in
finding the solution related to the quality problems of plastic gear. Therefore, the
fundamental issues of injection moulding will be reviewed in the next section.
2.5.1 Injection Moulding Process
Injection moulding is very common method used in plastic manufacturing
process, especially in producing complex parts and various sizes of mass production.
In facts, more than one third of all thermoplastic materials are manufactured in
injection moulding (Shen et al., 2007). According to Hill (1996), injection moulding
process can be defined as a forcing operation of hot molten polymer into the mould
system. Technically, the main parts of injection moulding machine are consists of
hopper, barrel, screw and mould. In view of in ection moulding process, it can
divided into four phase filling, packing, cooling and e ection ( ozdana
18
yerc oğlu, 2002). The beginning of process, the pellet or plastic granular from
hopper is dragged into the hot barrel. The plastic granular is melted due to heat on
barrel surface and the friction of the screw rotation. The reservoir of molten plastic
is accumulated in the barrel. Then, the molten plastic is injected by force pressure
rapidly through a nozzle into a mould cavity. Once the mould cavity is filled,
packing pressure is applied. The moulded part is solidified gradually in cooling
stage. When the product has reached a temperature below the solidification point,
the mould is opened and finally, the product instantly ejected by pusher.
Many of plastic manufacturers preferred the injection moulding method due
to the capability of machine running is continuous with low operating cost and also
provide a high quality product (Tsai et al., 2009). The credibility of injection
moulding method has proven in various plastic manufacturing products such as
medical equipment, electric-electronic devices, and automotive parts, which
exhibited an excellent dimension accuracy and good finished surface as well (Wong
et al., 2008). Therefore, injection moulding is reliable manufacturing method in
producing complex product like plastic gear.
Similar to any manufacturing process, there are some limitations associated
with injection moulding. An intensive effort is required in controlling the parameter
settings of injection moulding in order to achieve a good quality product. Galantucci
and Spina (2003) stated that quality of injection moulded product can be evaluated
based on dimensional stability, appearance and mechanical properties performance.
The dimensional stability is referring to size and shape of moulded part against the
shrinkage and warpage. Moreover, the product appearance is evaluated based on
aesthetics values of moulded part which free from any burn marks, weld lines, poor
19
surface finish, air traps and sink marks. Lastly, the mechanical properties of
moulded part can be tested in term of tensile strength, impact strength, elongation
and modulus elasticity.
The consistency quality of moulded part is a crucial aspect in manufacturing
process to satisfy the customer needs. However, there are many influence factors
that contribute to the occurrence of defect product. In facts, the different condition
of injection moulding process may lead a different condition of quality product.
Comprehending to these facts, the root cause of the product defect need to be studied
for further improvement and also optimize all possible defects as well.
2.5.2 Influential Factors on Injection Moulded Quality
According to Chang and Faison (2001), there are several factors need to be
considered in producing a good quality of plastic moulded product; material
selection, mould and product design, and processing parameters. The compatible
settings of material selection, mould design and processing parameters could be
reduces the percentage of defect in production. The explanation on how the factors
are contributes to the occurrence of defect will further discussed in next section.
a) Material Selection
Material selection is a crucial stage in designing the injection moulded
product. Based on statistic survey by Stress Engineering Services (2012), poor
material selection contributes 45% of product failures and it's give a substantial
impact on product's quality performance. There are many factors need to be
considered in selecting the material for product design. Jahan et al. (2010) emphasis
the selection of material is based on various aspect including function of product,
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material properties, processability, cost, constraint, environmental aspects and
aesthetics.
A few studies have been done to present the fundamental and theoretical for
selection procedure of material. Da Costa et al. (2006) analyzed the impact strength
on mixtures of ground scrap rubber tires (SRT) and polypropylene (PP); ethylene–
propylene–diene terpolymer (EPDM) and PP; and, ground SRT, PP and EPDM. The
finding shows, no major change on impact strength of mixed ground scrap rubber
tires (SRT), even it worse then unmixed condition. This is happened due to a poor
adhesion and large rubber particle size. Based on this study, the incompatibility of
material mixed may lead worse material performance.
Moreover, Kurokawa et al. (2003) studied the gear performance on four
different types of carbon fiber reinforced polyamide material; polyamide 12 (PA12),
polyamide 6 (PA6), polyamide 66 (PA66), and polyamide 46 (PA46). As a result, the
author found that material reinforced PA12 of gear shows a great performance in
sustaining high load capacity, noiseless operation and low water absorption.
Furthermore, Moa, et al. (2009) investigated the failure mechanism of gear friction
and wear behaviour. Two different materials, acetal and nylon were used and tested
under a same constant load. The results showed that acetal gear experienced worn on
tooth surface, whereas nylon gear has fractured at root and pitch. From this study,
the different material selection is clearly showing the different performance of
product.
Often, the material selection is done manually. It is very complicated and
expensive process due to various available materials is introduced every years and
the decision maker required a high knowledge and experiences. Today, the material
21
selection is not an issue anymore for manufacturer because the material information
is available in material data bank such as computer-aided engineering (CAD)
software and HyperQ/Plastics program (Beiter et al., 1993). The developed
programme software has offered better flexibility in selecting the correct material.
b) Mould System and Product Design
As known, the mould system is a main part in supporting the injection
moulding process. A bad design of mould system can lead to disastrous
consequences on the quality of produced part. Barrière, et al. (2002) emphasized that
mould and product design as well as injection parameter settings have a mutual
influences and interact each other. Therefore, understanding the mould operating
system includes its mouldablility of part geometry and parameter settings are
required in order to improve the product quality.
In the study of Kim et al. (2003), the gate position in mould design
significantly influence the flow pattern of injection molten plastic. The author
observed the resin flow pattern and modified by varying four different gate locations
of mould design in order to avoid the product failure such as short shots formed in
injection process. From this study, the short shots defect has overcome and the
molten plastic smoothly fills in the mould cavity. In another study, Demirer et al.
(2007) conducted an experiment to investigate the effects of runner system on
injection moulding process and properties of injected part. The author made a
comparison for both conditions of mould system, between the conventional runner
systems (CRS) and hot runner system (HRS). Findings of this study showed, the hot
runner system required low injection pressure in producing high weight product. The
22
shrinkage and warpage decreased with decreasing process temperature, increased
with decreasing injection pressure.
In view of product design, the performance and functionality of product can
be influenced by modification of product's geometry. Düzcükoğlu (2009) conducted
an experiment to observe the performance of modified and unmodified plastic gear
tooth width. The different loads were applied on gear rotation. The results showed
the wear damage on modified tooth gear has been delayed compared to unmodified
gear. This study has proven that product design significantly influenced the
performance of moulded product. Therefore, the plastic manufacturer must take into
account and should not be underestimated the contribution factor of the product and
mould design that affecting on the quality of moulded part.
c) Processing Parameters
Apart of material selection, mould and product design, parameter settings of
injection moulding is considered as a main contribution factor that affecting the
quality of moulded product. Due to the complexity of injection moulding process,
the variation of defects could be occurred on product such as short shots, shrinkage,
residual stress, warpage, burn mark and sink mark (Oktem et al., 2007). According
to Bryce (1996), there are four basic groups of processing parameters involved in
injection moulding; temperature, time, pressure and distance.
Many researches have been done to investigate the influence of injection
moulding parameters on the quality of the moulded part. Mehat and Kamaruddin
(2011) investigated the effects of injection moulding parameters on the mechanical
properties of recycled plastic toolbox tray. By considering six processing parameters,
the preliminary experiment was conducted via Moldflow Plastic Insight integrated
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with the L18 Taguchi orthogonal array (OA). Subsequently, the significant
parameters obtained from preliminary experiment were used to conduct a principal
experiment via L9 Taguchi OA. As a result, authors found that injection time is
significantly influence the flexural modulus of a recycled toolbox tray by percentage
contribution of 40.49% and the melting temperature is significantly influence the
yield stress with percentage contribution of 43.34%. Zhil’tsova et al. (2009) studied
the effect of filling rate, packing pressure, packing time and hot nozzle temperature
of the mould on the dimensional stability of high density polyethylene (HDPE)
acetabular cups. Findings showed the packing pressure is the most influential factor
on dimensional stability of HDPE acetabular cups.
In other study, Chen et al., (2009) reduced the warpage of moulded thin shell
plastic part. Four processing parameters were analysed via simulation and
experiment. The results obtained from both analyses were compared side-by-side.
As a result, authors found that melting temperature and packing pressure is the most
significant factors in contributing warpage on thin shell. Moreover, Ozcelik (2011)
optimized process parameters condition and weld line on the mechanical properties
of polypropylene (PP) mouldings. Three processing parameters have been considered
including melting temperature, packing pressure and injection pressure. The results
showed the injection pressure and melt temperature are the most important
parameters affecting the maximum tensile load and the extension at break.
In plastic gear making process, compatible injection parameter settings can
improve the quality of moulded gear. Mehat et al., (2012) optimized the process
parameter settings of injection moulding, in order to reduce the shrinkage of tooth
thickness, addendum and dedendum circle of moulded PP. Finding showed that
24
packing pressure, cooling time and packing time is the most significant injection
parameters that influenced the dimensional stability of moulded PP gear. In other
study of Mehat et al., (2013), the effects of process parameters settings including
melting temperature, packing pressure, packing time and cooling time have been
studied on properties of elongation and ultimate strength of PA6 plastic gear. The
results indicated that melting temperature, packing pressure, packing time and
cooling time have contributed to the variation performance of elongation and
ultimate strength of moulded PA6 gears.
Comprehending to case studies, the optimal processing parameter settings of
injection moulding is an important factor need to be considered in producing a better
quality moulded part. Therefore, a systematic optimization method is required to
facilitate the parameter settings. For better understanding on the optimization method
used in this research, detail explanation will further discuss in next section.
2.6 Optimization Method
As discussed in previous section, there are many influential factors that
affecting the injection moulded quality product; including inappropriate material
selection, poor mould and product design, and incompatible parameter settings.
However, this study emphasized the optimization of parameter settings in injection
moulding process in order to obtain the optimal performance of quality moulded
product. Therefore, the effectiveness and a reliable optimization method must be
applied to control the influential parameters and directly can improve the product's
quality performance.
Design of experiment (DOE) is one of common method used in designing
and optimizing the process control. In early 1920s, DOE was introduced by British